The National Academies Press

Currently Skimming:

7 Critical Knowledge Gaps
Pages 145-160

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.

From page 145... ... � Provides, where appropriate, recommendations to nar row these knowledge gaps � Discusses stakeholder acceptance of the more aggressive possible projects � Describes a conceptual alternative to the Third Delta that could reduce adverse stakeholder response It is appropriate in an overall project at this stage and of this magnitude, such as the LCA Study (U.S. Army Corps of Engineers, 2004a) Read the entire page →
From page 146... ... ; and the maintenance of a fixed water course for the Mississippi River and the associated losses of freshwater, nutrients, and sediments to deep water. Although it is understood that all of these are contributors, there was a surprising divergence of assessments by experts as discussed below. Read the entire page →
From page 147... ... Army Corps of Engineers, 2004a) Read the entire page →
From page 148... ... At the same time, steps will need to be made to resolve conflicts over ownership and use of the canals and compensation for their closure. Clearly, this becomes more than a simple engineering task and a more challenging target than diversions adjacent to the Mississippi River. Read the entire page →
From page 149... ... These processes include severely reduced sediment supply; barriers composed of a combination of muds, silts, and sands; high rates of relative sea level rise; and episodic severe storms. Because of the complexities of these processes and the relatively limited experience related to the level of barrier island construction and maintenance required, the predictability of the performance of these constructed systems is limited. Read the entire page →
From page 150... ... Identifying and Developing Restoration Methods with Low-Energy Requirements It is evident that energy costs and related constraints will continue to increase in the future. Thus, at the earliest possible stage of LCA Study development, a fundamental principle should be incorporated to select methods that will utilize the minimum amounts of energy to accomplish Read the entire page →
From page 151... ... HYDROLOGIC KNOWLEDGE GAPS The hydrologic processes can be divided into chronic and episodic knowledge gaps. The chronic knowledge gaps are the issues and processes that develop gradually over time and can be foreseen and accounted for within the Adaptive Environmental Assessment and Management Program. Read the entire page →
From page 152... ... are transported long distances in this manner. ment supply to an area that alters salinities or rates of relative sea level rise. Read the entire page →
From page 153... ... Another issue is how much of the current sediment discharge to the Gulf of Mexico can realistically be transferred to the coastal wetlands. To resolve these fundamental questions, detailed knowledge is required about the sediment delivery to coastal Louisiana (what proportion is derived from channel migration and bed scour or from transport from the upper Mississippi River) Read the entire page →
From page 154... ... These issues could have a major impact on the design considerations of created wetlands affecting the spatial area that can be restored and on the persistence of wetlands over time, as well as the amount of excess nutrients that can effectively be removed. SOCIETAL KNOWLEDGE GAPS Projections With and Without Project The State of Louisiana has initiated research directed at understanding the physical, chemical, and ecological processes in coastal Louisiana. Read the entire page →
From page 155... ... More generally, there is insufficient analysis of proposed enhancements in ecological services provided by proposed coastal restoration projects in the LCA Study or its supporting documents. The selection of projects is only marginally based on such services (e.g., storm protection) Read the entire page →
From page 156... ... If this decision could be made by all owners in a general area at the same time, it would be feasible to consider delivery of water and sediment by some means to reinstate or maintain elevations compared to relative sea level rise. However, even with this concession, the ongoing subsidence would require either a near continuous delivery of sediment to the area or an initial delivery that would increase the land elevation by several decimeters. Read the entire page →
From page 157... ... Two magnitudes of maximum peak flow are considered when the Mississippi River floods: 3,398 cubic meters (m3) per sec (4,444 cubic yards [yd3] Read the entire page →
From page 158... ... Explicit steps to address these gaps should be incorporated in the Science and Technology Program called for in the LCA Study. These gaps include the following: � The relative importance of various causes of land loss by area to more effectively target the solutions � The causes of loss and changes in the rate of loss to determine the long-term prospects of maintaining the coastal Louisiana ecosystem and the activities it supports � The role of growth fault reactivation in land loss to interpret past land loss patterns, predict future land loss rates and locations, and design strategies for land creation on the delta � The potential for various methods of sediment delivery over long distances (perhaps using existing dredging techniques) Read the entire page →
From page 159... ... CRITICAL KNOWLEDGE GAPS 159 � The factors to incorporate into a regional sediment budget to be able to use deterministic models effectively � The economic and societal toll of land loss used to justify, partially, the restoration of coastal Louisiana � Stakeholders' near- and long-term responses to gauge their acceptance of the restoration activities � The ecological and economic benefits of habitat shifts to better inform the project selection process � Quantification of the anticipated nutrient reduction, identification of the mechanisms and their relationship to different wetland habitats, and assessment of the consequences to the open ocean system to assess amelioration of hypoxia � Quantification of the anticipated risk reduction from hurricanes due to storm surge and wave activity Read the entire page →

From page 145...

... � Provides, where appropriate, recommendations to nar row these knowledge gaps � Discusses stakeholder acceptance of the more aggressive possible projects � Describes a conceptual alternative to the Third Delta that could reduce adverse stakeholder response It is appropriate in an overall project at this stage and of this magnitude, such as the LCA Study (U.S. Army Corps of Engineers, 2004a)

7 Critical Knowledge Gaps Pages 145-160

7 Critical Knowledge Gaps
Pages 145-160